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Chapter 8 Continental shelves!!!. Intro! Only 8% of global sea surface Mostly falls in the euphotic zone o Its shallow Areas that have narrow shelves.

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Presentation on theme: "Chapter 8 Continental shelves!!!. Intro! Only 8% of global sea surface Mostly falls in the euphotic zone o Its shallow Areas that have narrow shelves."— Presentation transcript:

1 Chapter 8 Continental shelves!!!

2 Intro! Only 8% of global sea surface Mostly falls in the euphotic zone o Its shallow Areas that have narrow shelves there is also upwelling which helps the production The shelves fuel of 90% world’s fisheries Are affected by human influences

3 Continental shelves! The shelf goes from the ­­­­­­­­­­­­extreme low-water mark on the shore line about 200 m deep Its considered neritic Continues till shelf break (anywhere from km offshore ) Usually has a shallow gradient of 1˚ Strongly influenced by physical forcing (physical processes like waves) because they are really close to shore Waves affect ecology of the shallower parts of the shelf Effects on benthic ecology go to about 80m Fetch is the uninterrupted distance over which winds exert friction at the sea surface

4 Currents and water… Currents are increased when a water mass moves through or around land bounded restrictions, or across irregularities in seabed topography o Straights and estuaries typically have typically have the strongest tides o Headlands and bedrock cause tides to be strong around the apex of the headland o Irregularities in seabed cause friction so the current slows down

5 Fronts! Fronts occur at a point where stratified water and mixed water meet Results in density gravity dient between the two bodies of water Causes an influx of nutrients Causes more productivity Can also happen near estuaries o mixing of waters with different densities. o Causes a frontal system o Can deflect the current away from the shore with aid from the Coriolis affect o Called Regions Of Freshwater Influence (ROFIs)

6 Depth and turbitity Depth and turbidity are important determining factors of the locations of benthic algae Areas affected by estuarine plumes are usually very light limited Caused by suspended sediment and photodetritus o These places are mostly lived in by animals Coastal areas that are open to the ocean are much clearer o Algae can be found almost everywhere there Clear zonation from the shallow water to the deeper o Green (shallow), brown, red (deep) o In these situations algae are dominant in biomass o Width of algae dominance depends on water clarity and slope of sea bed

7 Animals and stuff Processes vary with morphology of the seabed and coast Body size affects both production processes and how much a specific life form is associated with a specific place o Size of animals living on seabed is constrained by ability to burrow and respire o Size of attached animals are limited by physical processes Sheer due to current speed Mobility of organism varies o Highly mobile fish and o Anemones that can move a few mm a day o Others cemented to the rock Mobility affects the ability to respond to environmental change Places a limit on how much they can use the enviroment

8 More animals… Grouping are based on body size o Macrofauna Anything larger than meiofauna Most research has been done on them o Easiest to study o Meiofauna Organisms that would pass through a sieve with a mesh diameter of.5mm but would be restrained by mesh of.063 mm Least studied but most diverse Rates of production is much higher than larger macrofauna Make very indication of environmental stress

9 Yaaay.. Yet more animals Microbiota Contribution is often underrepresented o In tropics can be much greater than the others combined Body size and longevity are factors that affect recovery time Smaller organisms take less time to recover Organisms are also categorized by relative position on seabed

10 Things that live in sand… Epibiota organism Emergent organisms that are anchored in or on substratum or free living organisms that move on surface of substratum Algae are almost exclusively epibenthicGrow attached to substratum o Sometimes calcareous algae form their own habitats Infaunal organisms Live buried within substratum o Entirely o Partialy

11 Movement! Sessile organisms show seasonal patterns of growth at high latitudes Mobile organisms show varying level of inshore/ offshore movement due to temperature Many crabs and lobsters move inshore during spring and summer to find mates o Then move back during winter to avoid storms Distribution of bottom dwelling fish in regional seas are linked to certain habitat types

12 Yay fish and movement At mid-high latitudes fish are associated with a range of habitats o Variation can be attributed to different behavioral characteristics at different life stages Juveniles are vary picky of sediment grain sizes o Needs more protection o Limits places it can live Adults are less picky o They can live more places

13 Feeding Nearly all predators will also eat carrion o Even herbivorous sea urchins and suspension feeders will eat carrion They are known as facultative scavengers. (Will eat carrion if there is nothing else). Obligate scavengers are debated to exist. (Only eats carrion) o Candidates would have to be <6 mm o There have been lots of possible species but no conclusive evidence.

14 Food… again Maintain diversity within algal-dominated community. Herbivory in fish is more common toward lower Lat. In higher lat. Herbivores are mostly invertebrates. o In systems where a specific species is the predominant grazer they can have a key-stone role or eco-engineering role because they eat certain algae. Grazers also include carnivores Evolutionary arms race:race for one species to evolve into something that the predator can’t eat vs. the predator trying to evolve to beat those defenses

15 Feeding.. Yet again Filter Feeders: extract phytoplankton from water column and suspended mater from just above the seabed (suspension feeding) o Individual animal (about 1g dry weight) filters about 57 liters of water a day o Have an important role in Bento-pelagic coupling Waste is rich in organic material that is processed by microbial community which feeds the suspension feeders and bulk sediment processers

16 More things Organisms can have both a stabilizing and destabilizing role in communities. o Cumulative effect of all sediment disturbances known as bioterbation. They left what’s called trace fosils in rocks They enhance the passage of oxygen rich water deeper than into the sediment than it usually would go. Increases sediment porosity o Burrows made by high density organisms can expose 1.4 m 2 o Sediment conveyors- transfer nutrients deeper into the sediment

17 Cascades and stuff The flexibility in feeding patterns leads to compications o if you remove species from system, the system isn’t likely to cause significant cascade effects at either end. o Resilience can weaken when human interference and environmental change happen simultaneously. o Simple systems like this are expected in high diverse systems that are characterized by specilized feeding interactions o Interactions in cascades are between organisms from major trophic levels ithin systems(Predator-Herbivore-Primary producer) o Key predators or herbivores in trophic cascades are usually the dominent organisms in their trophic level

18 Organisms Often can be ecosystem-engineering biota. They are organisms that due to their abundance or feeding or other activities, exert a strong influence on the structure of the ecosystem When the link between one trophic level is strong that means that when there is a significant decrease in the pop of a predator/herbivore, there are few others to take their place Habitat is composed of : o Non biologic material Biogenic material Things that came from living things (broken shells) biota(living things) Prevailing water-column conditions above o Normally depends on interaction between seabed hardness and stability o Sediments dominate the seabed habitat of the continental shelf Very according to: o Tectonic history o quantity and quality of the inputs from rivers o transport by currents and waves

19 Surfaces Hard substrata is rather rare o Strata categorized as: hard (bedrock to cobble Soft (gravel to mud) Biogenic habitats Bedrock is most stable Provides an archer for sessile life forms o Occupied by crusting things Really important for algae o Creates the ability for kelp forrests Rocks with lots of relief, such as rock reefs also create microhabitats

20 Fooooood Dominated by particle feeders o The crevices permit the exchange well oxygenated water provide a hiding place from predators o Many species of fish use these places for refuge when they are growing up Fishery’s have tried to increase the available habitats by creating artifical reefs The size of substrata is mostly determined by physical processes and are subject to frequent disterbances o When the physical processes weaken and there are less physical forces There are more biological and chemical sediments o Stability of sedimentary habitats depends on interaction of physical, chemical and biological processes

21 Size of things in the ocean The size of substrata is mostly determined by physical processes and are subject to frequent disterbance o When the physical processes weaken and there are more fine sediments There are more biological and chemical sediments o Stability of sedimentary habitats depends on interaction of physical, chemical and biological processes Typically described by their partical size We can only get partial info from this technique Doesn’t tell us about how the different types of sediment pack together o We can’t tell the porosity or anything that we can learn from knowing the porosity

22 Sediments… yaay.. Near-shore sediments less than 30m deep are often moved by wave actions o Almost no sessile life forms o Highly mobile organisms most common In deeper water (more than 50m deep) or in shallow sheltered areas: o Finer sediments settle out due to redused physical forcing o Lots of burrowing amimals that shape seafloor o Mostly crustaceans and shrimp live here Many semi-enclosed seas and fjordic areas have mud communities o Weak currents o Sheltered o Heavy stratification durring summer

23 Reefs…. kinda…. o Can be made entirely by reef building organisms Formed by bivalves, corals (hermatypic vs. ahermatypic) and sponges Can be made by accumulations of things, inorganic or organic material

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